University:
Boston University
Course:
CAS CH 524 | Chemical Biology Laboratory
Academic year:

2023
Views:

479

Pages:

4
Author:

paproszekmca5

TP Which of the following is correct about water? 20% 1. 20% 2. 20% 3. 20% 4. 20% 5. The low enthalpy of vaporization results in a low vapor pressure at room temperature The high enthalpy of vaporization results in a low vapor pressure at room temperature The low enthalpy of vaporization results in a high vapor pressure at room temperature The high enthalpy of vaporization results in a high vapor pressure at room temperature There is no simple relationship between vapor pressure and enthalpy of vaporization For today … • Postscript: Vapor pressure and boiling • Intermolecular forces • Hydrogen bonding 1 TP Which of the following is correct about water? Enthalpy change of vaporization, ∆vapH 20% 1. 20% 2. 20% 3. 20% 4. H2O NH3 N2 ⇌ H2O , Δvap ⇌ NH3 , Δvap ⇌ N2 , Δvap 40.7 kJ/mol at 100 ˚C 23.3 kJ/mol at 78 ˚C 5.6 kJ/mol at 196 ˚C etc. 20% 5. 3 The low enthalpy of vaporization results in a low vapor pressure at room temperature The high enthalpy of vaporization results in a low vapor pressure at room temperature The low enthalpy of vaporization results in a high vapor pressure at room temperature The high enthalpy of vaporization results in a high vapor pressure at room temperature There is no simple relationship between vapor pressure and enthalpy of vaporization 4 1 Intramolecular and intermolecular forces TP Which of the following are associated with intramolecular forces forces within a molecule ? Intermolecular forces are forces of attraction between molecules 13% 13% 13% 13% 13% 13% 13% 13% Chemical changes are related to breaking and formation of covalent bonds due to intramolecular forces within molecules. Physical changes are governed by intermolecular forces 1. 2. 3. 4. 5. 6. 7. 8. Fog forms on a cold morning Wet clothes are hung out to dry Ice melts 1 and 2 1 and 3 2 and 3 All of the above None of the above 5 6 Intermolecular forces: stickiness! A molecules attract one another, because of the attraction of opposite electrical charges. Hydrogen bonding Most specific and strongest is “hydrogen bonding”: X—H ∙ ∙ ∙ Y More common and intermediate strength is “dipole‐dipole attraction”: Always present and weakest is “temporary dipole attraction” “dispersion interaction” : 7 11 2 Ice and water Ice and water 13 Effect of T on water density 14 Hydrogen bond angle is 180° Why does the density rise from 0 ˚C to 4 ˚C? Why does the density fall from 4 ˚C to higher temperatures? 18 19 3 Hydrogen bonds are longer than typical bonds Which of the following cannot form H bonds? • Ammonia, NH3 • Methanol, CH3OH • Ethanol, CH3CH2OH • Dimethyl ether, CH3OCH3 20 21 Quiz Which of the following cannot form hydrogen bonds with themselves? 0% 0% 0% 0% 0% 0% 0% 0% 1. 2. 3. 4. 5. 6. 7. 8. Ammonia, NH3 Methanol, CH3OH Ethanol, CH3CH2OH Dimethyl ether, CH3OCH3 1 and 3 1 and 4 2 and 4 All of the above can form hydrogen bonds with themselves 22 4